This invention relates to an electrically insulating structurally strong bushing assembly, for electronic equipment and, more particularly, the invention is concerned with providing an electrically insulating, structurally strong bushing assembly for use at the mounting interface of an electronic chassis requiring a single point electrical ground.
As a general rule, electronic equipment, especially analog type electronics such as the Low Power RF units, cannot tolerate the usual multi-point random type of grounding within the chassis enclosure. This type of uncontrolled grounding results in an increase in electrical noises which is often found to be the reason for the failure of the system phase noise tests. In order to control the ground paths, the ground must be established at only one pre-determined location, usually in the area of the rear guide pin bushings or at the bolted front surface of the chassis. However, this generates a problem with the mounting of the chassis to a radar equipment rack. The chassis mounting points must be able to structurally withstand the vibration and shock environments to which the radar equipment is subjected. These mounting points must also have the capability to withstand the shock impact of the chassis sliding into the rack and being positioned by the steel pins in the rack.
The hereinafter described electrically insulating structurally strong bushing assembly provides a specially machined epoxy-glass bushing which is capable of providing electrical insulation with a steel insert which is capable of providing the required high strength. The epoxy-glass bushings are machined from plate stock with the grain direction running perpendicular to the structural load. This machining specification results in a 60,000 psi allowable bearing load compared to only 30,000 psi for conventional epoxy-glass. With the steel insert in position, this unique bushing assembly permits single point grounding of the chassis while simultaneously being capable of withstanding vibration and shock load inputs to the chassis.